1. Field of the Invention
The present invention relates to image data processing apparatuses and, more particularly, to an image data processing apparatus for delaying image data having a plurality of parallel bits which represent tones.
2. Description of the Related Art
Conventionally, images in two colors are often formed simultaneously in a digital copying machine, a laser printer, or the like.
For example, in a copying machine, it is possible to set a simultaneous bicolor mode wherein an image of the original is scanned once to form an image of a particular part in the image of the original in red and an image of the other parts in black.
Such an image forming apparatus is constructed so that two chargers and two developing devices with different colors of toner are arranged respectively in positions facing an outer peripheral surface of a photoreceptor drum and shifted away from each other in a circumferential direction, and respective laser beams from two laser beam sources driven by different image data are irradiated to the photoreceptor drum in positions behind the respective chargers to perform exposure.
The positions on the photoreceptor drum exposed by the respective laser beam sources are shifted away from each other in the circumferential direction, so that it is necessary to delay image data to one of the laser beam sources which exposes a position backward in the direction of rotation of the photoreceptor drum by a time required for the photoreceptor drum to rotate therebetween as compared with image data to the other laser beam source, and an image data delaying apparatus is used for doing that.
A conventional image data delaying apparatus is constructed so that image data is once stored in a delay memory, and, after a lapse of a required time, the image data is read from the delay memory disclosed (Japanese Patent Laying-Open No. 2-145367 (1990), for example).
Although the capacity required for a delay memory is increased according to the number of bits of image data, i.e. the number of tones, the number of tones is conventionally determined fixedly during designing of the apparatus.
Specifically, the capacity of a delay memory is determined fixedly according to the number of tones in a conventional image data delaying apparatus. Therefore, it is not easy and is actually impossible to change the number of tones, especially to increase the capacity of the delay memory in order to increase the number of tones.
Therefore, in a case where it is desired to enhance the number of tones in a stage wherein a copying machine or a laser printer is used, large-scale remodeling, exchanging of printed board units all over the image data delaying apparatus, is required.